The trim or lining parts referenced in this disclosure include a surface skin that is flexible to the touch, an intermediate layer made of a foamed or cellular substance, and a rigid support layer.
In various implementations of trim or lining parts, one may integrate one or more additional surface element(s) partially or completely embedded in the thickness of the surface skin (flush or projecting element). The addition of such may be provided for decorative and/or functional reasons.
Vehicle users and manufacturers demand certain preferences, which may frustrate production. The demands may be related to aesthetic, technical and economic constraints and/or demands. For example, the demands may be related to:                providing an embedding as well as an optimal finish between the flexible skin and the additional elements added to the surface in the skin with zero gap between the skin and each element (absence of a visible groove, mounting with zero tolerance) and with an effect of continuity on the visible surface of the part (if applicable, perfectly flush between the surface of the skin and the surface of the additional element);        providing an option of variations in terms of appearance, shape and material for the additional elements, without impacting the production tools, particularly the skin shaping mold (which is a shell for producing the skin by the so-called “slush” method or by spraying of PU) and the foaming mold;        being able to attach additional elements even when the configuration, the topology and/or the local geometry of the part is/are unfavorable for such attachment in an obvious manner;        being able to reduce or limit the complexity of the manufacturing method;        being able to reduce the costs of the tools and/or the cost prices of the parts;        being able to put in place a plurality (two, three, four or more) of additional elements at separate or even mutually distant sites, even when these elements are of small size;        being able to produce parts with and without additional element in the same foaming mold (or with minimal modification of the latter) and/or without additional element in the mold for shaping the skin with just-in-time production management.        
Various techniques are already known that make it possible to mount additional elements, in the form of surface inserts, on parts of the above-mentioned type.
For example, in document WO 2013/026571, a method for producing an interior lining part formed by a support body covered with a decorative layer is disclosed.
The support body has an indented area produced by molding or obtained by deformation to receive by insertion an additional element having a complementary shape. The integral securing of this insert is carried out or reinforced by an anchoring points that engages in the material of the support body.
However, this involves a different mold shape for each different shape of additional element or each different installation site for these elements. In addition, the additional elements comprise beveled side walls and the support body becomes fragile due to the installation of anchoring points.
In another example, in document FR 2 937 276, a method for manufacturing a dashboard comprising a decorative element is disclosed. In the context of this method, a skin is first formed in a shaping mold with creation of an indentation or of a recess, by placement of a functional insert. This formed skin is then transferred to a foaming mold in which the intermediate foam layer is produced and the functional insert is then replaced by a decorative insert having the same shape.
Nevertheless, the replacement of the inserts is possible only for particular shapes and it does not make it possible to guarantee zero peripheral interstices between the final insert and the skin, or a reliable maintaining of said final decorative insert over time.
In another example, in document WO 2010/046600, a method is known for manufacturing dashboards of the type mentioned in the introduction, in which the additional element in the form of a decorative part is mounted in a cut out portion of the skin.
Specifically, the additional element includes a peripheral shoulder which abuts against the internal or back wall of the skin, along the contour of the cut-out produced beforehand in the latter. The skin provided with this element is then arranged in the foaming mold to produce the intermediate layer.
This solution requires the presence of a shoulder over the entire periphery of the additional element, which constitutes a major manufacturing constraint and limits the possible shapes for the additional element. In addition, it is no longer possible to guarantee the sealing of the cut-out, since it depends both on the positioning of the additional element in the cut and on the manner in which the foaming develops during the manufacturing of the intermediate layer.
Also disclosed is a technique for mounting on the surface functional and/or decorative inserts by encapsulation of the latter by the skin (a technique called “inskin” and described in particular in the document FR 2 894 868).
This technique consists of heating the skin before arranging it in the foaming mold, the insert having been arranged beforehand between the skin and the wall of the mold. Then, the skin is applied by suction against the wall in such a manner that the insert becomes embedded in the skin. The manufacturing of the part is then completed by foaming the intermediate layer.
This technical solution may not be employed for certain skin molding technologies when the base material is a powder (for example, the so-called “slush molding” method) or an excessively fluid chemical substance (for example, spraying of PU), or when the mold has to be brought to a high temperature (for example, “slush molding”: 300° C.), or when the skin shaping mold has to perform prohibitory movements (for example, rotation in rotational molding for “slush molding”).